Lamp assemblies incorporating reflectors are well known. Examples include spotlights and floodlights for indoor and outdoor use. A lamp is mounted in a sealed outer envelope which includes a reflecting interior surface, typically parabolic, for directing light in a preferred direction. The reflector is covered with a lens, and a base is provided for mounting the lamp assembly and for interconnection of the lamp assembly to an electrical energy source. Incandescent lamps, high-pressure sodium arc tubes and mercury arc tubes have been utilized in such lamp assemblies.
Recently, it has been proposed to utilize metal halide arc tubes in reflector lamp assemblies. Metal halide arc tubes provide excellent color, long life and high efficiency. Low wattage metal halide arc tube assemblies include an arc tube which encloses a suitable fill material such as sodium, scandium and mercury iodides. Electrodes are located within the arc tube at opposite ends, and electrode leads extend through press seals for connection to an electrical source. An example of a reflector lamp assembly utilizing a metal halide arc tube is disclosed in U.S. Pat. No. 4,961,019, issued Oct. 2, 1990 to White et al.
It has been found desirable to mount metal halide arc tubes within a light-transmissive quartz shroud or shield. The shroud produces a higher and more uniform arc tube temperature than would otherwise occur. The shroud is, in part, responsible for the excellent color temperature and the long operating life of metal halide arc lamps. In addition, it is known that metal halide arc tubes are subject to burst on rare occasions. The shroud contains shards of the arc tube when the burst occurs.
When a metal halide arc tube is mounted in a reflector, several requirements must be met. It is preferred, in order to maximize light output, that the axis of the arc tube be aligned with the optical axis of the reflector and that the center of light output of the arc tube coincide with the focal point of the reflector. The mounting arrangement for the arc tube must provide means for mounting both the shroud and the arc tube. The arc tube and the shroud must be securely mounted within the lamp envelope to prevent damage during shipping and handling.
In conventional arc discharge lamps which utilize a bulbous lamp envelope, the arc tube and shroud are mechanically supported from both ends of the lamp envelope. However, the process of fabricating a reflector lamp assembly involves heating steps which cause the reflector to sag under the weight of the lens. Later in the process, a pressurized gas is introduced into the lamp envelope in order to raise the lens to a desired height. This variation in dimensions during processing precludes the mount assembly for the arc tube and shroud from being secured to the lens.
It is well known that conductors located in proximity to an arc discharge tube containing sodium cause sodium migration, or sodium electrolysis. Sodium ions migrate through the wall of the arc tube and thereby reduce the life of the lamp. It has been found desirable to keep conducting frame members and power leads away from the arc tube to the extent possible. In prior lamp assemblies which do not include a reflector, a frameless construction has been utilized in which a fine wire connects the arc tube electrode at the dome end of the lamp to the electrical feedthrough at the base end of the lamp. The arc tube is maintained in position by bulb spacers at the base and dome ends of the lamp envelope. The electrically-isolated floating frame develops a positive charge which inhibits the migration of sodium ions through the arc tube. As noted above, a double-ended mechanical mount is not feasible in a reflector lamp assembly.
It is a general object of the present invention to provide improved reflector lamp assemblies.
It is another object of the present invention to provide reflector lamp assemblies which utilize metal halide arc discharge tubes.
It is a further object of the present invention to provide a metal halide reflector lamp assembly having a long operating life.
It is a further object of the present invention to provide a lamp assembly, including a metal halide arc tube and a light-transmissive shroud, suitable for mounting in a reflector.
It is yet another object of the present invention to provide a metal halide lamp assembly wherein all conductive parts except the electrical inleads are electrically isolated.
It is yet another object of the present invention to provide a metal halide reflector lamp assembly that is compatible with automatic assembly equipment.
It is still another of the present invention to provide a metal halide reflector lamp assembly that is capable of withstanding mechanical shock and vibration during routine shipping and handling.
It is a further object of the present invention to provide a lamp assembly, including a metal halide arc tube mounted in a reflector, that is easily manufactured and low in cost.